I used Flitz to slightly polish the damascus blade on one of my MCusta knives. That knife came from the factory with brown stains (some form of oxidation) on the blade. I put a dab of Flitz on a paper towel, then rubbed the blade down for a few minutes. The damascus lightened up quite a bit, but the layers are still visible and it looks a lot better.
If you do an extensive polishing job with the Flitz, the blade will become more uniformly silver, with less contrast between the layers. That will look a lot like the damascus scales on the steel handled Mcusta knives that Ive seen, where there arent really any dark layers.
On my other MCusta knife, the etching is a little uneven, so there are some areas that are a bit blacker than they should be. (I thats the situation youre describing, dannyv.) That personally doesnt bother me though. I know it will probably never really look perfect, so Im just not going to fool with it.
One thing to watch out for when using Flitz is that you dont want to spend too much time polishing one spot on the blade. That can create shiny, irregular splotches on the finish. Also, the stamp on the blade that says MCUSTA is actually etched on and Flitz will remove it pretty quickly.